This invention relates to a combinatorial weighing system and, more particularly, to a combinatorial weighing method and apparatus through which it is possible to select, in a short period of time, a combination of articles having a total combined weight value within preset allowable limits and closest to a preset weight value.
A combinatorial weighing apparatus has a plurality of weighing machines each consisting of a weighing hopper and a weight sensor associated with the weighing hopper. According to a known combinatorial weighing method using the aforesaid apparatus, combinatorial weighing is carried out by weighing articles which have been introduced into the weighing hoppers of the weighing machines, selecting the combination of weighing machines (referred to as the "optimum" combination) that gives a total weight value equal to a preset value or closest to the preset value within preset allowable limits, discharging only those articles contained by the weighing hoppers of the selected weighing machines, and subsequently replenishing the emptied weighing hoppers with new articles to prepare for the next weighing cycle. The foregoing sequence of steps is repeated to carry out a continuous, highly accurate weighing operation automatically.
FIGS. 1 and 2 illustrate a combinatorial weighing apparatus for practicing the above-described weighing method. FIG. 1 shows the apparatus in diagrammatic form, and FIG. 2 is a block diagram of a combination control unit.
Referring to FIG. 1, numeral 1 denotes a main feeder of vibratory conveyance type. Articles to be weighed are introduced into the main feeder 1 and imparted with vibratory motion for a predetermined length of time so as to be dispersed radially outward from the center of the main feeder. Numerals 2, 2 . . . denote n-number of weighing stations which are arranged around the main feeder 1 along radially extending lines to receive the articles dispersed by the main feeder. Each weighing station 2 includes a dispersing feeder 2a, a pool hopper 2b, a pool hopper gate 2c, a weighing hopper 2d, a weight sensor 2e, and a weighing hopper gate 2f. The dispersing feeder 2a comprises an independently vibratable conveyance device for feeding the articles by means of vibration, or an independently operable shutter. In either case, each dispersing feeder 2a is so arranged that the articles received from the centrally located main feeder 1 can be introduced into the corresponding pool hopper 2b disposed below each dispersing feeder 2a. The pool hopper gate 2c is provided on each pool hopper 2b in such a manner that the articles received in the pool hopper 2b are released into the weighing hopper 2d when the pool hopper gate 2c is opened. Each weighing machine is composed of with an attached weighing hopper 2d and a weight sensor 2e. The weight sensor 2e is operable to measure the weight of the articles introduced into the weighing hopper 2d of the weighing machine, and to apply an electrical signal indicative of the measured weight to the combination control unit 5 shown in FIG. 2. The combination control unit then selects the combination of articles (the "optimum" combination) which gives a total weight equal to a preset value or closest to the preset value within preset allowable limits, as will be described below in further detail. Each weighing hopper 2d is provided with its own weighing hopper gate 2f. A drive controller, shown in FIG. 2, upon receiving the signals from each of the weight sensors, produces a signal to open only the weighing hopper gates 2f of those weighing hoppers 2d that give the optimum combination, these gates 2f discharging the articles from the corresponding weighing hoppers 2d into a common chute 3 where they are collected together. The collecting chute 3 has the shape of a funnel and is so arranged as to receive the articles from any of the circularly arrayed weighing hoppers 2d via the hopper gates 2f, which are located above the funnel substantially along its outer rim. The articles received by the collecting chute 3 are collected at the centrally located lower end of the chute 3 by falling under their own weight or by being forcibly shifted along the inclined wall of the funnel by a mechanical scraper or the like (not shown). The collecting chute 3 is provided with a timing hopper 4 at the lower end of chute 3 for temporarily holding the collected articles. The arrival of an externally applied release signal from a packaging machine or the like causes the timing hopper 4 to release the retained articles from the system.
Reference will now be had to the block diagram of FIG. 2 for a description of one example of the combination control unit. The combination control unit 5 includes an n-bit (n=10) counter 5a for counting timing pulses TP of a predetermined frequency, and for generating all combinations of n-number of the weighing hoppers. These combinations will also be referred to as "combination patterns" where appropriate. Specifically, for n-number of weighing hoppers, n combinations are possible when each combination is composed of one weighing hopper from the total of n weighing hoppers, n(n-1)/2! combinations are possible wehn each combination is composed of two weighing hoppers selected from said total, and, in general, n(n-1) (n-2) . . . (n-r+1)/r! combinations are possible when each combination is composed of r-number of weighing hoppers selected from said total of n weighing hoppers. Accordingly, when the n-bit binary counter 5a has counted 2.sup.n -1 timing pulses TP, a total of 2.sup.n -1 different bit patterns, from 000 . . . 001 to 111 . . . 111, will have been generated. Therefore, if correspondence is established between the first bit and the first weighing hopper, between the second bit and the second weighing hopper, and between third through n-th bits and the third through n-th weighing hoppers, then the generated bit pattern will be an indication of the above-mentioned combination pattern.
A multiplexer 5b, in accordance with the output bit pattern of the counter 5a, provides an arithmetic unit 5f with weight values (indicative of the weight of the article batches) from the weight sensors 2e of weighing hoppers designated by the bit pattern of the counted value in counter 5a. For instance, if the value of the count (the bit pattern) in counter 5a is 1000101011 when n=10, then the arithmetic unit 5f will receive, as inputs, the weight value outputs W1, W2, W4, W6, W10 from the weight sensors 2e attached to the first, second, fourth, sixth and tenth weighing machines, respectively. A register 5c is provided for storing a preset value Wa. Numerals 5d, 5e denote upper and lower limit setting devices, respectively, for storing preset allowable limits (namely an upper limit or maximum value Ma, and a lower limit or minimum value Mi, respectively) which are desirable for weight values. The minimum value Mi is set equal to the target value, as is customary. If it were set lower than the target value, the result could be delivery of articles having a total weight less than that intended, and complaints might ensue.
The arithmetic unit 5f computes, and delivers a signal indicative of, the total weight .SIGMA. Wi (=X) of the weight values received from the multiplexer, and also computes the difference between the total weight .SIGMA. Wi and the preset value Wa. The arithmetic unit 5f produces a signal A indicting the absolute value of the computed difference. More specifically, the arithmetic unit 5a performs the operations: EQU .SIGMA.Wi=X (1) EQU .vertline..SIGMA.Wi-Wa.vertline.=A (2)
and produces a signal representing the total weight .SIGMA. Wi (=X), as well as a signal A representing the absolute value (hereafter referred to simply as the "deviation") of the difference between the total weight .SIGMA. Wi and the preset value Wa. The value X is applied to a comparator 5g, whose output is connected to a proper weight counter 5h. The comparator 5g discriminates whether the total weight value X lies in the range defined by Mi and Ma. Specifically, if the following relation holds: EQU Mi.ltoreq.X.ltoreq.Ma (3)
then the comparator 5g will increment (count up) the counter 5h by one. A minimum deviation register 5j for storing the minimum deviation is set automatically to the deviation A the first time only, and thereafter is updated as the conditions warrant, as will be described later. In the case where the minimum value Mi is set equal to the preset value, it is permissible to initially set the minimum deviation register 5j to the difference between the maximum value Ma and the preset value. An optimum combination memory 5k is adapted to store the optimum combination pattern. Numerals 5m and 5n denote gates. When the total weight value .SIGMA. W.sub.i is within the preset allowable limits, a comparator 5p compares the deviation value A, namely the output of the arithmetic unit 5f, with the prevailing minimum deviation value, denoted by B, stored in the minimum deviation register 5j. When the inequality A&lt;B holds, the output of comparator 5p is such that the deviation value A is delivered for storage to the minimum deviation register 5j through the gate 5m, and the content (combination pattern) of counter 5a is delivered for storage to the optimum combination memory 5k.
When the state of counter 5h is one or more, the drive controller 6, which receives a signal from memory 5k indicative of the optimum combination pattern, is operable to open the weighing hopper gates 2f (FIG. 1) specified by the optimum combination pattern, so that the corresponding weighing hoppers discharge their articles into the collecting chute 3, and to open the corresponding pool hopper gates 2c so that the emptied weighing hoppers may be replenished with articles.
The operation of the weighing apparatus will now be described. At the start of operation, each of the pool hoppers 2b and each of the weighing hoppers 2d contain a supply of articles. The weight sensors 2e provided on corresponding ones of the weighing hoppers 2d measure the weights of the articles and produce weight values W1 through W10 which are sent to the multiplexer 5b. The n-bit (n=10) counter 5a counts the timing pulses TP having the predetermined frequency to produce 2.sup.n -1 combination patterns. Thus, when the first timing pulse TP arrives and is counted, the state of counter 5a becomes 0000000001. As a result, the multiplexer 5b sends the first weight value signal W1, from the weight sensor 2e provided on the first weighing hopper 2d, to the arithmetic circuit 5f, which responds by performing the operations specified by equations (1) and (2) above, thereby producing the signals indicative of the total weight .SIGMA. W.sub.i of the combination and of the deviation A (=.vertline.W1 -Wa.vertline.) between .SIGMA. Wi and the preset value Wa. Since the gates 5n, 5m will be open for the initial combinatorial computation, the deviation value A is transferred to and stored in the minimum deviation register 5j, and the content (the combination pattern 0000000001) of n-bit counter 5a is stored in the optimum combination memory 5k. Comparator 5g compares the total weight .SIGMA. Wi (=X) against the maximum value Ma and the minimum value Mi, and increments the counter 5h when the relation M.sub.i .ltoreq.X.ltoreq.M.sub.a holds. Thenceforth, when the second timing pulse TP is generated, the pulse is counted by counter 5a, whose state (combination pattern) is incremented to 0000000010. Consequently, the weight value output W2 of the weight sensor 2e provided on the second weighing hopper is delivered to the arithmetic unit 5f which then performs the operations of equations (1) and (2) to produce the signals indicative of the total weight .SIGMA. Wi (=X) and of the deviation value A (A=.vertline.W2-Wa.vertline.). The comparator 5g then determines whether relation (3) is satisfied; if it is, then the state of the proper weight counter 5h is incremented by one. The comparator 5p, meanwhile, compares the deviation value A with the state B (=.vertline.W1-Wa.vertline.) of the minimum deviation register 5j. If the relation A.gtoreq.B holds, then neither the register 5j nor the optimum combination memory 5k is updated; if A.ltoreq.B holds, the deviation value A is transferred to and stored in register 5j, and the state of counter 5a is transferred to and stored in the optimum combination memory 5k. The operation described above is repeated until all 2.sup.n -1 combinations have been generated. At such time the content of the minimum deviation register 5j will be the minimum deviation value obtained from the 2.sup.n -1 combinations, and the content of the optimum combination memory 5k will be the combination pattern that gave said minimum value. The optimum combination is thus selected from the total of 2.sup.n -1 possible combination patters.
If the value of the count in counter 5h is one or more, the drive controller 5k opens the weighing hopper gates 2f of weighing machines corresponding to the "1" bits of the input combination pattern (namely the optimum combination pattern), whereby the articles in these weighing hoppers 2d constituting the optimum combination are discharged into the collecting chute 3, after which the drive controller 5k opens the corresponding pool hopper gates 2c to replenish the emptied weighing hoppers 2d with articles. Further, the dispersing feeders 2a corresponding to the emptied pool hoppers are vibrated for a fixed length of time to resupply these pool hoppers with articles.
This completes one combinatorial weighing cycle, which may be repeated as often as required, to provide batches of the articles, each batch having a total weight equal or closest to the preset value. It should be noted that when the state of the proper weight counter 5h is zero in the foregoing operation, articles are not discharged and each of the weighing machines must be supplemented with articles to resume the combinatorial computations.
Thus, the combinatorial weighing method described above is extremely useful in obtaining a combination of weighing machines giving batches of articles having a total weight closest to a preset value within a preset allowable range, these article batches then being discharged from the system. However, a disadvantage with the above conventional method is that a considerable period of time is required for execution of the computations. The reason is that the combinatorial computations are performed covering all 2.sup.n -1 possible combinations, that is, even those combinations which give a total weight far from the set value.